@model Foo
To: @Model.To
Subject: Welcome User
Views: Html, Text

public class FooEmailService : IIdentityMessageService
{
    public Task SendAsync(IdentityMessage message)
    {
        if (message == null)
            throw new ArgumentNullException("message");

        FooEmailBase email;
        switch (message.Subject)
        {
            case "NewUser":
                email = new NewUser { To = message.Destination, Link = message.Body};
                break;
            //omitted some codes
        }

        return email.SendAsync();
    }
}